docs: def fields_from_dict(d):
          """Load the fields from the dict, return a list with all the fields."""
          class_container = FieldsContainer.class_container
          fields = [field_cls.from_dict(field_dict) 
                    for field_cls, container in class_container.iteritems()
                    for field_dict in d.get(container, [])]
          return fields